The present invention related to lead-acid batteries and more particularly to improvements in gel electrolytes and separator materials for use therein.
A gel may be regarded as a type of colloidal system behaving as a solid or relatively low elasticity. Various attempts have been made to gel the acidic electrolyte in storage battery cells to eliminate spilling, the need for constant maintenance and for other reasons. No satisfactory gel electrolyte has been produced, however, because batteries containing such gel electrolytes have not had electrical properties as good as those with ordinary liquid electrolytes. For example, their internal resistance is higher and capacity is lower in batteries incorporating a gel electrolyte. Also, the cycling characteristics of batteries containing the gel electrolyte have not compared well with batteries having liquid electrolytes. In addition to these disadvantages, gel electrolytes have had a tendency to shrink after a short time so that the contact between the gel electrolyte and the active mass in the battery cell is soon interrupted. Thus, cracks form in the gel electrolyte allowing air to carry oxygen to the plates or electrodes of the battery, allowing the electrodes to discharge. Furthermore, the initial viscosity of the gel is so great that it has been difficult, if not impossible, to completely fill the electrolyte chamber and the electrode pores with the gel electrolyte.
One such attempt at gelling an electrolyte was disclosed in British Pat. No. 785,848, issued to Robinson on Nov. 6, 1957. This patent discloses the use of fine particles of silica of submicron size, approximately 0.015 micron diameter, mixed with dilute sulfuric acid. The amount of silica in the final mixture is disclosed to be about 12% by weight. However, the problems described above still remain.
Another problem which affects the use of both liquid and gel electrolytes is the need to replace the electrolyte after formation of the cell. Presently, most lead-acid batteries are filled with low specific gravity electrolyte and the electrodes of the batteries are formed by placing a charge on them. After this formation process, the formation electrolyte is dumped out and is replaced with fresh electrolyte having the desired specific gravity. It is well known that if the low specific gravity formation electrolyte were not replaced, the battery would exhibit poor electrical properties.
The formation process is expensive for a number of reasons. Changing electrolyte after charging requires additional labor and time. Even though the formation electrolyte may be recycled, contaminants build up in the electrolyte. Eventually, the electrolyte must be either cleaned or discarded.
It is well known that separator material is placed between electrodes of batteries to prevent electrical shorting. Simultaneously, the separator material must also permit diffusion of electrolyte through its pores and the passage of electric current between the electrodes of batteries to prevent electrical shorting. Simultaneously, the separator material must also permit diffusion of electrolyte through its pores and the passage of electric current between the electrodes. Additionally, the separator material must be stable in the electrochemical environment, i.e., resist deterioration due to exposure to the electrolyte and the chemical reactions taking place on the electrodes. One of the long standing problems in improving batteries has been to make a separator material which optimized those various characteristics.